Patent Literatures 1 to 3 and Non Patent Literature 1 each describe a reflectance variable element including a gap, across which paired electrodes are disposed so as to face each other, an electrolytic solution with metal ions dispersed therein being charged in the gap. In the reflectance variable element, upon application of a voltage between the paired electrodes, metal ions in the electrolytic solution can move to one of the electrodes and be deposited on the electrode, and upon cancellation of the voltage application to the paired electrodes or application of a reverse voltage between the paired electrodes in this state, the metal ions can be desorbed from the electrode.
Each of the elements described in Patent Literature 1 and Non Patent Literature 1 uses DMSO (dimethylsulfoxide) as a solvent. In the case of these elements, an electrolytic solution is prepared by dissolving AgNO3 as an electrochromic material, TBABr as a supporting electrolyte and CuCl2 as a mediator, respectively, in this solvent, and PVB (polyvinyl butyral) is added to the electrolytic solution as a polymer.
In the case of the element described in Patent Literature 2, a mixed solvent of DMSO and another solvent is used and an electrolytic solution is prepared by dissolving a metal salt of sliver such as AgF, AgCl, AgBr, AgI or AgSCN in the mixed solvent.
In the case of the element described in Patent Literature 3, an electrolytic solution is prepared by dissolving NiCl2 in dehydrated methanol, mixing this solution into a tetra ethyl ammonium tetra fluoroborate-propylene carbonate solution adding ferrocene to this mixed solution.